This invention relates to an automatic climate control for a vehicle heating, ventilation and air-conditioning (HVAC) system, and more particularly to a method of regulating HVAC control parameters based on an estimate of the heating or cooling power required to maintain the vehicle cabin temperature at a set temperature selected by a vehicle occupant.
In general, an automatic climate control system controls the HVAC control parameters (such as discharge air velocity, temperature and location) based on a desired cabin temperature (referred to herein as the set temperature) and a number of easily measured or estimated parameters such as the outside air temperature, the actual cabin air temperature, and the solar intensity. If the HVAC control parameters are correctly determined, the cabin air temperature will be brought into conformance with the set temperature and then maintained approximately equal to the set temperature despite variations in outside temperature and solar intensity.
Although various methods have been developed for determining the HVAC control parameters, the most physically-based approach is one in which the required heating or cooling effort is estimated based on a thermal loading model for the cabin, and appropriate control parameters for providing the required heating or cooling effort are then selected. The thermal loading model will typically include an ambient component characterizing heat transfer between the cabin and the outside air, a deep mass or core component characterizing heat transfer between the cabin air and the core elements of the cabin (seats, floor mass, etc.), and a solar component characterizing the net solar radiation into the cabin. When the ambient and core temperatures are referenced to the set temperature, the sum of the above-mentioned heat transfer components represents the heating or cooling effort required to maintain the cabin air temperature at the set temperature. In most cases, the required heating or cooling effort may be satisfied by any of a number of different combinations of discharge air temperature and velocity, and the control must include some method of determining which of the potential combinations of discharge air temperature and velocity is most appropriate.
Representative examples of the above-described control approach are disclosed in the U.S. Pat. Nos. 5,400,963 and 5,603,226 to Ishikawa et al., U.S. Pat. Nos. 5,988,517 and 6,173,902 to Bauer et al., and U.S. Pat. Nos. 5,832,990 and 5,995,889 to Eisenhour. Although the controls described in these patents embody a physical basis for determining the required heating or cooling effort under steady-state conditions, it is apparent that steady-state conditions rarely occur outside the laboratory or testing chamber. For example, both the outside air temperature and the solar radiation are subject to frequent and unpredictable variation. Accordingly, control parameters based on assumed steady-state conditions usually fail to maintain the cabin air temperature at the set temperature, and the actual cabin air temperature tends to oscillate around the set temperature. Accordingly, what is needed is an improved physically-based control approach that comprehends the dynamic nature of external conditions that influence cabin thermal loading, and that more faithfully regulates the cabin air temperature at the set temperature.
The present invention is directed to an improved motor vehicle automatic climate control method which determines HVAC parameter values for satisfying the required heating or cooling effort for steady-state cabin air temperature regulation, and controls the HVAC settings based on such parameter values and on the deviation of the cabin air temperature (Tcabin) from the set temperature (TSET). If Tcabin is within a specified control band about TSET, the HVAC settings are controlled in accordance with the determined HVAC parameter values, but when Tcabin overshoots or undershoots the control band, the control enters a quasi-steady-state mode in which the control parameters are reset to drive Tcabin back in to the control band, and then brought into correspondence with the respective determined values based on the degree to which the overall control objective of regulating Tcabin at TSET is achieved.